Evidence for growth of collective excitations in glasses at low temperatures

TL;DR

This study investigates the low-temperature acoustic response of glasses under electric fields, revealing evidence of collective excitations that challenge existing models and suggest increased interactions among two-level systems as temperature decreases.

Contribution

The paper provides experimental evidence of collective effects in glasses at low temperatures, highlighting the limitations of current dipole gap models and proposing increased TLS interactions.

Findings

Acoustic and dielectric responses show similar field dependence.

Temperature dependence of acoustic response is stronger than dielectric response.

Results suggest increased TLS collective effects at lower temperatures.

Abstract

We present new data on the nonequilibrium acoustic response of glasses to an applied dc electric field below 1K. When compared with the analogous dielectric response of the same material, the acoustic data show, within experimental precision, identical dependence on the perturbing field, but stronger temperature dependence. These data are difficult to reconcile with simple generalizations of the dipole gap model of two-level system (TLS) dielectric response, unless we assume that as T is decreased, interaction-based TLS collective effects increase.